This invention relates to an electric rotary power tool apparatus, holdable by hand during its operation, and operated with the aid of an electric current from an automobile battery or similar current source. Power tool apparatus of this kind are known to be supplied with energy from an automobile battery of 6 or 12 volts.
In a first aspect the invention relates to novel power tool apparatus usable as impact wrench for the loosening of seized or jammed parts, in particular of bolts and nuts of automobile wheels. In a second aspect the invention relates to novel power tool apparatus adapted particularly for use in hobby work.
In U.S. Pat. No. 3,977,278 granted on Aug. 31, 1976 to John Van Jackson, there is described an automobile electric impact wrench comprising, in a housing, an electric motor the shaft of which carries a tool socket, cable means for supplying electric power to the motor and being provided with connector means for engaging the two terminals of an auto battery as well as switch means interposed between the cable means and the motor. This power tool apparatus also comprises an impact-inducing speed-reducing gear train off the planetary type and of intermittent or ratcheting action, but without an impactor mass other than that of the motor. While, in this known apparatus impact is induced in the speed-reducer, this would require a very strong and heavy motor, impacting after each ratcheting, in order to yield sufficient impacts on the tool socket for loosening bolts and nuts of an automobile wheel, in particular for exchanging tires.
This power tool apparatus of Van Jackson only carries a tool connected via the impact-initiating speed reducing gear train to the end of the driven shaft of the tool socket. In order to lay out the Van Jackson motor for dimensions permitting successful use as an impact wrench for loosening severely jammed or seized bolts or nuts of automobile wheels or like parts, the seize and weight of the motor would have to be excessively large and, moreover, such motor would produce such large amounts of heat that special cooling means for the motor would have to be provided which would further increase the cost and weight of the entire apparatus.
In order to carry out "hobby" work, for instance thread-cutting, drilling, impact drilling, cutting and the like Mitsubishi Electric Europe GmbH, in 4030 Ratingen(West), Germany has already described in a pamphlet published in July, 1981 a number of power tool apparatus having weights ranging from about 0.9 to 1.7 kilograms which are supplied with electric energy from nickel-cadmium batteries of 4 to 8 cells and a direct voltage of from 4.8 to 9.6 volts. Impact drills of this type have a frequency of 10,000 impacts per minute, and idling speeds of from about 250 to 1000 r.p.m. of the motor, and a torque of from 250 to 500 Newtoncentimeters (Ncm).
These apparatus, however, are relatively weak, and unsatisfactory for tightening or loosening heavy duty bolts and nuts such as are used in mounting automobile wheels of passenger cars or trucks (lorries) on their wheel hubs.
Such heavier duty work can, however, be carried out with impact wrenches manufactured by Robert Bosch GmbH, Leichterfelden, Germany, as published in a prospectus "Bosch Elektrowerkzeuge" of August 1981, in particular those of Types 1430, 1431 and 1432. Energy for these apparatus must however be supplied alternating electric current, taken from a city electric main, and having of from about 110 to 240 volts. These apparatus are much heavier than the "hobby types mentioned hereinbefore; they weigh about 3 to 8 kilograms. They have a speed of the driven shaft at full load of about 500 to 1000 r.p.m., an output of 165 to 360 watts and a tightening torque of about 180 to 800 Newtonmeters (Nm), corresponding to about 18 to about 80 meter-kiloponds (mkp).
Of these known power tool apparatus, not even the last-mentioned, main-connected impact wrenches but only heavier impact wrenches which work with compressed air and thus require much more complicated arrangements including a compressor, may be able to solve the particular problems which arise in loosening jammed or seized bolts or nuts of automobile wheels when these parts have not been loosened for a long time and/or have been excessively tightened so that they have eaten into the material containing the threaded bores or bolts. Seizing of such parts may also be due to rust or dirt or the like causes. Moreover, switch means and speed control means of known types for the kind of power tool apparatus, dimensioned so that it could be connected to an auto battery or the like source of electric current, and which are laid out in accordance with known techniques, are very large und unwieldy.
Moreover, the versatility of the known hand-held apparatus is not very great being essentially limited to normal and emergency work on automobiles, and in particular as impact wrench, and whereas the known apparatus is configured to supply sufficient electric torque to serve as an impact wrench while being operated with electric current from a car battery, no switches and no speed control means have thus far been described to my knowledge that would not be of excessive size and weight for reasonably comfortable handling.
Thus, conventional on-off and reversing switches laid out for a direct current electro-motor operated by electric direct current of the initially mentioned characteristics, especially when of the permanent magnet type, would be far too large to be housed in the handle of a power tool apparatus and also be far too heavy to be held comfortably by the user's hands during use. Unless such switches of known type and involving, for instance, magnetic coils, are built too large and of relatively heavy parts, there would be danger of overheating of the switch, resulting in decrease and/or irregularities in the power output of the motor, and possibly even melting of wires in the switch.
There has also appeared on the market in the United States a 12 volt-impact wrench, Model No. 9518, sold by Black & Decker (U.S.) Inc. Raleigh, N.C. 27625. This impact wrench is destined to be connected with a 12 volt battery. The specifications given are: 12.6 volt D.C., 19 amps, up to 100 ft. lbs. (136 Nm) of torque, 1/2 in. square drive, 1100 impacts (revolutions?) per minute, forward/reverse switch, 17 ft. cord, ball & sleeve bearings. This impact wrench has a net weight of 75/8 lbs. and is said to be usuable with an average size battery in good condition. As far as I know this impact wrench represents the closest prior art and has therefor been used in. Its comparative tests to be described further below its speed-reducing ratio is 15:1.